# For the Lagrangian of fermion masses, how do I understand?

1. Jun 20, 2015

### lhcQFT

Hello, everyone.

I have a one question which is related to the fermion masses.
If you see my latex mathematics, you can know what I want to say.
Here, L means SU(2) left-handed lepton doublets and R means SU(2) right-handed lepton singlets.

So I am too much confusing to understand this mechanism. When I expanded lagrangian into components of lepton doublets and that of lepton singlets, I can't understand how these terms( (1x1) (2x2) (1x1) <= I expressed each term by using matrix notation ) can be gauge singlets? If you give me detailed explanation, I really thanks to you.

Have a good day.

2. Jun 20, 2015

what latex?